In the case of semiconductor components which are used in so-called “harsh environments,” the bonding islands, which are formed on the component surface, and the bonding wires, which are used for electrical contacting, are subjected to extreme environmental conditions, such as particularly high or low pressures, particularly high or low temperatures, and/or chemically aggressive media.
The use of pressure sensor elements for monitoring the soot particle filter of a motor vehicle is mentioned here as an example of such an application. For this purpose, the pressure sensors are situated in the exhaust system of the motor vehicle upstream and downstream from the soot particle filter. The load of the soot particle filter may be determined and the burn-off of the filter may be regulated on the basis of the differential pressure.
Corrosion of the bonding islands and bonding wires impairs the electrical contacting of a semiconductor component and therefore its functionality. In order to prevent this, in practice, bonding islands and bonding wires made of gold are typically used for contacting semiconductor components which are intended for use in aggressive measuring media. In addition thereto, the contact areas are frequently also gelled, which limits the possible packaging forms for the semiconductor component, however. In addition, the material properties of the gels used may change due to aging, whereby their protective effect typically decreases.
A layer structure for electrical contacting of a piezoresistive pressure sensor element is described in European Patent No. EP 1 760 442, which was implemented starting from a silicon substrate. The piezoresistors are integrated together with connecting lines into the substrate surface. The substrate surface has been passivated to protect the circuit elements. For this purpose, a silicon dioxide layer was produced as the first passivation layer on the substrate surface and a second passivation layer was produced above it in the form of a silicon nitride or silicon carbide layer. The sensor element is electrically contacted here via an opening in the two passivation layers in the area of the connecting line. For this purpose, an ohmic contact layer made of platinum silicide or tantalum silicide is produced in the surface doping of the connecting line. A dense tantalum or niobium layer is located above it, which functions as an electrically conductive adhesive layer for a noble metal layer. The bonding islands for the electrical contacting of the sensor element are formed in this noble metal layer. The adhesive layer and the noble metal layer accordingly extend over the opening area of the passivation layers, in which the ohmic contact layer is formed, up to the areas of the component surface in which bonding pads are to be situated.
This layer structure has proven to be problematic in multiple aspects when the semiconductor component is used in a chemically aggressive environment. Thus, at temperatures above 150° C., damage of the tantalum or niobium adhesive layer may occur, which may even result in the failure of the component. In addition, the noble metal layer forms a galvanic cell together with the electrically conductive tantalum or niobium adhesive layer in a chemically aggressive medium, if the tantalum or niobium adhesive layer comes into contact with the medium at any point of the component surface, for example, in the edge area of the layer structure or due to layer defects. The conversion of chemical energy into electrical energy occurring in this case also has an impairing effect on the functional capability of the component.